How Do You Size a Transformer?
Quick answer — Size a transformer by summing the connected load, adding the diversity and any future growth, and allowing for the power factor and the step voltage. The kVA/MVA rating = (connected load kW) / power factor, adjusted for diversity and a margin, so the unit can serve the peak and allow a small overload reserve. The voltage, impedance and vector group are set by the network and the system. A design tool (or calculator) does the per-unit check.
How do you calculate the rating of a transformer?
Estimate the load
Sum the connected load, apply the diversity so the co-incident demand is used, add the expected growth, and account for the motor inrush and any special load.
Convert to kVA
Divide the real load (kW) by the power factor to get the kVA, and add a margin for the load and the voltage (and a small overload reserve).
Set the rest
Choose the voltage ratio, impedance, vector group and cooling to match the network and the application, then check the regulation and the fault level.
References & standards
- IEC 60076-1
- IEEE C57.12.00
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
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Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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